The Iraq war was just the first of this century's "resource wars", in which powerful countries use force to secure valuable commodities, according to the UK government's former chief scientific adviser. Sir David King predicts that with population growth, natural resources dwindling, and seas rising due to climate change, the squeeze on the planet will lead to more conflict.

"Future historians might look back on our particular recent past and see the Iraq war as the first of the conflicts of this kind - the first of the resource wars," he told an audience of 400 in London as he delivered the British Humanist Association's Darwin Day lecture.

Implicitly rejecting the US and British governments' claim they went to war to remove Saddam Hussein and search for weapons of mass destruction, he said the US had in reality been very concerned about energy security and supply, because of its reliance on foreign oil from unstable states. "Casting its eye around the world - there was Iraq," he said.

This strategy could also be used to find and keep supplies of other essentials, such as minerals, water and fertile land, he added. "Unless we get to grips with this problem globally, we potentially are going to lead ourselves into a situation where large, powerful nations will secure resources for their own people at the expense of others."

King was the UK government's chief scientific adviser in the run-up to the start of Iraq war in March 2003, but said he did not express his view of its true motivation to Tony Blair. "It was certainly the view that I held at the time, and I think it is fair to say a view that quite a few people in government held," said King, who is now director of the Smith School of Enterprise and the Environment at Oxford University.

However, before the war loomed he had made an effort to persuade the Bush administration to adopt more climate-friendly policies. "I went into the White House in 2001 to persuade them that de-carbonising their economy was the way forward. I didn't get much shrift at that time. What I can tell you is that, if I had managed to persuade the government of America that investing (instead of going into Iraq) in de-carbonising their economy with roughly a tenth of [the estimated $3 trillion the US spent on the war], they would have managed it."

Commenting on the idea of "resource wars", Alex Evans, of the Centre for International Co-operation at New York University, who last month wrote a report on food security for the Chatham House thinktank, said he believed King was right, but overly pessimistic. "You always get conflict over the allocation of scarce resources," he said. "The question is whether it is violent conflict ... If the political system can't cope, that's when it gets violent."

King's lecture - Can British Science Rise to the Challenges of the 21st Century? - also warned politicians not to allow the financial crisis to distract them from tackling climate change. "I would like to see [in] every speech Gordon Brown makes on the fiscal crisis, that he also includes the global warming crisis," he said, but added: "It's fine for the prime minister to make a good speech on climate change, but you need all members of the cabinet, because reducing carbon by 80% by 2050 will require every part of government to respond."

King summed up by saying that with growing population and dwindling resources, fundamental changes to the global economy and society were necessary. "Consumerism has been a wonderful model for growing up economies in the 20th century. Is that model fit for purpose in the 21st century, when resource shortage is our biggest challenge?"